Discovery of the Electron, Models & Theories

Discovery of the
Electron, Models &
JJ Thompson Robert Millikan
• Discovered the electron
• Wrote books on atomic
theory and structure
• First to suggest that
atoms have parts
• Found the accurate way
to decide the charge
carried with an atom
Niels Bohr
• Helped create a picture
of the atomic
structure(Bohr model)
• This said that electrons
orbit the nucleus in
fixed circular orbits
Louis de Broglie
• Looked into Bohr’s
investigation and
thought electrons
moved in waves rather
that circular orbits
Werner Heisenberg
• Known for his theory in
quantum mechanics
• Proved Bohr’s theory
wrong about the
movement of electrons
• Said we can’t assign to
an electron a position in
space at a given time,
nor follow it in its orbit
Erwin Schrodinger
• Developed a waveequation that
accurately gave
energy levels to
Bohr Model
An atom consisting of small positively charged nucleus orbited by negatively
charged electrons
Similar to planetary model where planets orbit the Sun
Solar system uses gravitational forces whereas an atom uses electrostatic forces
Electrons have certain orbits with certain radii
Orbits are circular according to quantized energy levels
Orbits with larger radii have larger energies
Quantum Model
 Based on quantum theory, which says matter also has
properties associated with waves
 Impossible to know the exact position and momentum
of an electron at the same time
 Uses complex shapes of orbitals (electron clouds)
volumes of space in which there is likely to be an
 Based on probability rather than certainty
 Thompson experimented with cathode rays and magnets that led to the
discovery of the electron
 Millikan devised an oil-drop experiment where he’d drop tiny charged
droplets to find out their specific charge
 Bohr based his model on experiments done by Ernest Rutherford; he saw
Rutherford’s model wasn’t quite right and changed it
 Broglie saw that Bohr’s model, specifically the electrons, move in waves,
not in a circular orbit
 Heisenberg also went off of Bohr’s model and elaborated more into
quantum mechanics to explain the wave motion of electrons instead of a
circular orbit
 Schrodinger used mathematical equations to predict the likelihood of
finding the electron and eventually found one that worked
Time Line of History
 Scientists from the early 1900s
 Theories developed without use of more precise
modern technology
Over time…
 Bohr’s model had a lot of problems and inaccuracies
to it
 Quantum model is considered “standard” and is also
considered the most accurate physical theory ever

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